1. Field
The subject matter presented herein relates generally to wireless identification systems that use electronically sensitive tags to store and provide identification information, and more particularly, to an identification system that employs a directed-energy device as a tag reader.
2. Description of Related Art
Radio Frequency Identification (RFID) systems can be used in a variety of industries to identify, track and provide various other types of information related to the items upon which the tag is placed. A typical RFID system can include at least one transmitting and receiving device, commonly called a reader, and at least one passive or active target device, commonly called a tag or transponder. A basic principal of operation of an RFID system involves the transmission of radio frequency (RF) energy from the reader to the tag. The tag can receive the signal, modify the energy, and reflect the modified signal back to the reader where the reflected and modified return signal can be received, read and decoded. The reader can contain antennae for receiving information from the tag.
RFID tags can contain at least two parts. One can be an integrated circuit for storing and processing information, modulating and demodulating an RF signal, and other specialized functions. The second part can be an antenna for receiving and transmitting the signal.
When an RFID tag passes through a field of a scanning antenna associated with a reader, it can detect an activation signal from the antenna. An activation signal can “wake up” or excite the RFID tag, allowing the RFID tag to transmit information on its microchip and to be received by the scanning antenna of the reader.
In some instances, the tags can have their own internal power source (active tag). Passive RFID tags have no internal power supply. The minute electrical current induced in an antenna in the tag by the incoming RF signal can provide enough power for a, e.g., CMOS integrated circuit in the tag to power up and transmit a response. Passive tags can signal by backscattering the carrier wave from the reader. This means that an antenna structure in the RFID can be designed both to collect power from the incoming signal and to transmit the outbound backscatter signal. The response of a passive RFID tag may not necessarily be just an ID number; the tag chip can contain non-volatile data, possibly even a writable EEPROM for storing data.
The transmission of information and power between the reader and the tag can typically be accomplished by the modulation of the RF carrier. In these instances, a reader can be maintained in the ON state to provide power to passive tags and/or can be pulsed off and on for short intervals to receive the information from active and passive tags.
Common issues with RFID systems can include reader collision and tag collision. Reader collision can occur when the signals from two or more readers overlap. The tag may be unable to respond to simultaneous queries. Systems can be carefully set up to avoid this problem. Tag collision can occur when many tags are present in a small area.
Another issue with RFID devices is range. RFID devices can typically work within a few feet (up to 20 feet for high-frequency devices, for example) of a scanner/reader. Various factors can affect the distance at which an identification tag can be read (the read range). The frequency used for identification, the antenna gain, the orientation and polarization of the reader antenna and the transponder antenna, as well as the placement of the tag on the object to be identified can have an impact on the RFID tag system's read range.
On a different note, the configuration and operation of directed energy devices varies widely as is illustrated by the disclosures within U.S. Pat. Nos. 6,809,307; 6,784,408; 6,849,841; 6,864,825 and 7,126,530, which are incorporated herein by reference in their entirety.